1. Field of the Invention
The present invention relates to an image forming apparatus and signal processing apparatus using a frequency dispersion technique for continuously modulating oscillation frequency.
2. Related Background Art
Most image forming apparatuses are designed to control operations of individual units thereof using control and drive clocks generated based on clocks with high oscillation accuracy.
However, regulations that require suppression of radiation noise produced by the operation of image forming apparatuses are becoming increasingly strict each year. As a counter measure to such regulations, frequency dispersion techniques that intentionally lower apparent oscillation accuracy are known. The frequency dispersion technique has an effect of integrally lowering a radiation noise peak by periodically and continuously changing the oscillation frequency. Since the phase relationship among various control and drive clocks, which clocks are generated based on a frequency-dispersed clock signal, is maintained, normal operation can be assured in a digital system, except for special cases.
However, when frequency dispersion is used in analog signal processes, and an output signal from a device such as a CCD line sensor, which is driven by a digital clock signal and outputs an analog signal waveform associated with the phase relationship among the clock signals and pulse width, is to be processed, beat noise that responds to the period of frequency dispersion is produced. The beat noise results from the influences of data variations of the output signal waveform of the CCD line sensor and of sampling positions that change slightly under the influences of the period of frequency dispersion and frequency dispersion of the drive clock signal of the CCD line sensor. Further, when beat noise asynchronous with a reference signal is present during image formation, an image resulting from the beat noise unwantedly forms on image formation.
It is an object of the present invention to attain satisfactory image formation by suppressing production of beat noise upon processing image data by using the frequency dispersion technique.
It is another object of the present invention to correct any slight deviation of a modulation period produced as a result of using the frequency dispersion technique, and to stabilize the operation level while maintaining the reduced radiation noise level.
In order to achieve the above objects, an image forming apparatus according to one aspect of the present invention comprises image reading means for reading image data, oscillation means for oscillating a reference clock at predetermined periods, frequency dispersion means for generating a clock signal having a frequency higher than a frequency of the reference clock using the reference clock, and continuously changing the frequency of the generated clock signal at the predetermined periods with respect to the frequency of the reference clock, control clock generation means for generating a control clock using the clock signal, the frequency of which is continuously changed by the frequency dispersion means, and reset means for resetting the continuous change in frequency of the clock signal by the frequency dispersion means at a read timing of the image reading means.
A clock generation device according to another aspect comprises a plurality of oscillation output means for performing frequency dispersion that continuously changes an oscillation frequency at predetermined periods with respect to a reference clock, and a plurality of reset means for resetting the frequency dispersion of the plurality of oscillation output means in accordance with a reference signal generated based on the reference clock.
An analog signal processing device according to still another aspect comprises a clock generator for generating a control clock by performing frequency dispersion that continuously changes an oscillation frequency at predetermined periods with respect to a reference clock, an analog signal processing unit for processing a predetermined analog signal in accordance with the control clock, and correction means for correcting an error in a modulation period between the control clock and the analog signal, which error is produced by frequency dispersion of the clock generator.
An image forming apparatus according to still another aspect comprises a plurality of oscillation output means for generating drive and control clocks by performing frequency dispersion that continuously changes an oscillation frequency at predetermined periods with respect to a reference clock, image reading means for reading an image in accordance with the drive clock, signal processing means for performing a process that pertains to image formation with respect to an output signal from the image reading means in accordance with the control clock, and correction means for correcting an error in a modulation period between the control clock and the output signal from the image reading means, which error is produced by frequency dispersion of the plurality of oscillation output means.
With these arrangements, images can be satisfactorily formed while suppressing production of beat noise. Also, any slight deviation of the modulation period can be corrected, and the operation level can be stabilized while maintaining the reduced radiation noise level.
The foregoing and other objects, advantages and features of the present invention will become more apparent from the following detailed description of the preferred embodiments taken in conjunction with the accompanying drawings.